1-10 Minute Timer ProjectThe circuit starts timing when switched
on. The green LED lights to show that timing is in progress.When
the time period is over the green LED turns off, the red LED turns
on and the bleeper sounds.The time period is set by adjusting the
variable resistor and it can be adjusted from 1 to about 10
minutes.Please note that the range of time periods is only
approximate. With perfect components the maximumtime period should
be 4 minutes, but this is typically extended to about 10 minutes
because the 220Ftiming capacitor slowly leaks charge. This is a
problem with all electrolytic capacitors, but some leakmore than
others. In addition the actual value of electrolytic capacitors can
vary by as much as 30% oftheir rated value.
Parts Required resistors: 470, 33k, 100k 555 timer IC variable
resistor: 1M 8-pin DIL socket for IC capacitors: 0.1F, 220F 16V
radial on/off switch LEDs: red, green battery clip for 9V PP3
bleeper 9-12V stripboard 10 rows 22 holes
